Ink compositions containing lanthanide complexes

ABSTRACT

The invention relates to an ink composition containing (a) a compound of formula (I), L m -Ln 3+ (Ch − ) n  (I), wherein Ln represents a lanthanide, CH −  is a negatively charged ligand containing at least one UV absorbing double bond, n denotes 3 or 4, m denotes a number from 1 to 4, in case n is 3, m denotes a number from 1 to 4 and L is a neutral monodentate or polydentate nitrogen-, oxygen- or sulfur-containing UV absorbing ligand with the exception of 2,2′-bipyridyl or, in case n is 4, m denotes 1 and L is a single-charged cation; and (b) a liquid ink carrier, which can be used for applying hidden mark on objects which can only be revealed under UV exposure.

The present invention relates to ink compositions containinglanthanide^(III) complexes, a system for marking items with a hiddenmark and a method for providing hidden marks on objects.

There is a need for applying hidden marks which can only be revealedunder UV exposure on a variety of articles for several reasons.

Thus, security markings are needed on envelopes, checks, bank-billsshares, securities, stamps, identity cards, passports, tickets,certificates etc.

Textiles are also furnished with such covert designs which may act assecurity markings or as special decorations which only become visibleunder UV radiation.

WO 97/10307 discloses a jet ink composition suitable for marking onwhite or light coloured substrates comprising an ink carrier and afluorescent colorant which is a rare earth metal organic chelate. Thosefluorescent colorants are excitable in the UV radiation in the range offrom about 275 nm to about 400 nm and fluoresce in the visible range.However, the intensity of the luminescence and the quantum yield do notmeet the most superior requirements.

It is therefore an object of the present Invention to provide an inkcomposition comprising a colorant which is invisible to the unaided eyebut yields a strong luminescence under UV exposure and which compositioncan be used for all known printing applications on various substratessuch as textiles including leather, cellulosic materials, metals,plastic materials, other substrates coated with an oligomeric orpolymeric matrix and other porous materials.

The invention relates to an ink composition containing

-   (a) a compound of formula I    L _(m) −L _(n) ³⁺(Ch⁻)_(n)  (I),-    wherein Ln represents a lanthanide,-   Ch⁻ is a negatively charged ligand containing at least one UV    absorbing double bond, n denotes 3 or 4, m denotes a number from 1    to 4,-   in case n is 3, m denotes a number from 1 to 4 and L is a neutral    monodentate or polydentate nitrogen-, oxygen- or sulfur-containing    UV absorbing ligand with the exception of 2,2′-bipyridyl or, in case    n is 4, m denotes 1 and L is a single-charged cation; and-   (b) a liquid ink carrier.

The compounds of formula I can basically contain any monodentate orpolydentate nitrogen-, oxygen- or sulfur-containing UV absorbing ligandsuch as, for example, unsubstituted or substituted pyridine, pyrazine,quinoline, aniline, phenanthroline, terpyridine, imidazole,benzimidazole, bisimidazole, bisbenzimidazole, pyrimidine, bipyrimidine,naphthyridine, triazine, bistriazine, oxazole, bisoxazole, oxazoline,bisoxazoline and substituted derivatives thereof and all relevant(poly)N-oxide derivatives of above cited ligands.

Since L can be a polychelating ligand, like for example 4,4′-bipyridyl,the compounds of formula I and II include multimetallic chelates, suchas for example the compound of formula (XIV), containing twoM^(III)-(diketone)₃ or M^(III)-(carboxylate)₃ units connected via abidentate ligand:

Preferred ink compositions contain as component (a) a compound offormula II, III or IV

 L_(m)-Ln³⁺[R₁—O]_(n)  (IV),

-   wherein Ln represents a lanthanide,-   n denotes 3 or 4, m denotes a number from 1 to 4-   in case n is 3, m denotes a number from 1 to 4 and L is a neutral    monodentate or polydentate nitrogen-, oxygen- or sulfur-containing    UV-absorbing ligand with the exception of 2,2′-bipyridyl or, in case    n is 4, m denotes 1 and L is a single-charged cation,-   R₂, is hydrogen or C₁-C₆alkyl, and-   R₁ and R₃ are each independently of the other hydrogen, C₁-C₆alkyl,    CF₃, C₅-C₂₄aryl or C₄-C₂₄heteroaryl.

Preferably L is a nitrogen-containing ligand.

Particularly preferred are compounds of formula I, wherein L is acompound of formula V, VI, VII, VIII or IX

wherein R₄, R₅ and R₆ are each independently of the other hydrogen,halogen, C₁-C₆alkyl, C₅-C₂₄aryl, C₆-C₂₄aralkyl, C₁-C₆alkoxy,dialkylamino or a cyclic amino group and R₇ is hydrogen, C₁-C₆alkyl,C₅-C₂₄aryl or C₆-C₂₄aralkyl.

Alkyl groups as substituents R₁ to R₇ can be straight-chain or branched.Examples that may be mentioned are methyl, ethyl, n-propyl, isopropyl,n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl,isopentyl, n-hexyl and isohexyl.

Alkoxy groups as substituents R₄ to R₆ can be, for example, methoxy,ethoxy, n-propoxy, isopropoxy, n-butoxy or tert-butoxy.

Examples of C₅-C₂₄aryl groups are phenyl, tolyl, mesityl, isityl,diphenyl, naphthyl and anthryl. Phenyl is preferred.

Heteroaryl group preferably contain 4 or 5 C atoms and one or twoheteroatoms selected from O, S and N. Examples are pyrrolyl, furanyl,thiophenyl, oxazolyl, thiazolyl, pyridyl, pyrazinyl, pyrimidinyl,pyridazinyl, indolyl, purinyl or chinolyl.

Aralkyl groups as substituents R₄ to R₇ can be, for example, benzyl,2-phenylethyl, tolylmethyl, mesitylmethyl and 4-chlorophenylmethyl.

Suitable dialkylamino groups are, for example, diethylamino,diisopropylamino, di-n-propylamino, N-methyl-N-ethylamino and, inparticular, dimethylamino or pyrrolidino.

Suitable cyclic amino groups are pyrrolidino and piperidino.

Halogen atoms as substituents R₄ to R₆ are preferably fluorine, chlorineor bromine, but in particular chlorine.

Preferred ink compositions according to the invention contain ascomponent (a) a compound of formula I, wherein L is a compound offormula V, VI, VII, VIII or IX wherein R₄, R₅ and R₆ are hydrogen,methyl, dimethylamino or pyrrolidino.

Preferred components (a) are compounds of formula I wherein Ln is Eu, Tbor Dy.

Furthermore, compounds of formula II, III or IV are preferred, whereinR₁ and R₃ are methyl, t-butyl, n-pentyl or phenyl.

R₂ in formula II is preferably hydrogen.

Particularly preferred as component (a) are the compounds of formula X,XI, XII, XIII, XIV or XV.

For certain applications it is recommendable to use a combination ofdifferent lanthanides, for example Eu and Tb. Such a mixture increasesthe degree of security of the hidden marks, the sophistication of thesecurity level and multiplies the coding possibilities.

The compounds of formula I are known, for instance from WO 96/20942, orcan be prepared by methods known per se. For example, a ligand such asacetylacetone, benzoylacetone, dibenzoylmethane, dipivaloylmethane,salicylic acid, valeric acid or caproic acid can be reacted undersuitable conditions with a rare earth metal halide such as europiumtrichloride to produce the rare earth metal chelate. Further details canbe found in U.S. Pat. No. 4,736,425.

The rare earth metal chelate so obtained can be further reacted with themonodentate or polydentate nitrogen-, oxygen- or sulfur-containingligand L thus yielding the rare earth metal chelate compounds of formulaII, III and IV.

This reaction is described, for example, in WO 96/20942.

Any suitable ink carrier known in the art of printing compositions,including aqueous and organic carriers and combinations thereof, can beused to prepare the ink compositions of the present invention. Thecarrier should have sufficient solubility for the compounds of formula Ior II and, where appropriate, for the additional ingredients of the inkcompositions. In addition, the carrier should be easily dissipatablefrom the printed article by evaporation and/or absorption in thesubstrate. Suitable organic carriers include alcohols, glycols, etheralcohols, sulfoxides, amides, amines, heterocyclic solvents, ketones,ethers, esters, nitrites and aliphatic, cycloaliphatic and aromatichydrocarbons.

Examples of suitable organic solvents are methanol, ethanol, n-propanol,isopropanol, n-butanol, glycerol, ethylene glycol, propylene glycol,diethylene glycol, dipropylene glycol, polyethylene glycol,polypropylene glycol, ethylene glycol monoethylether, ethoxybutanol,dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide(DMA), N-methylpyrrolidone (NMP), acetone, 2-butanone, diethylether,di-n-propylether, tetrahydrofurane (THF), ethyl acetate, ethylpropionate, acetonitrile, pyridine, n-pentane, n-hexane, cyclohexane,benzene and toluene.

Preferably the ink carrier (b) is an organic solvent, a mixture of twoor more organic solvents or a mixture of water and one ore more organicsolvents.

For solvent-based applications it is advisable to employ alcohols,ketones, esters, polyethers or aromatic hydrocarbons or mixtures of theaforementioned solvents as ink carrier.

Solvents which are miscible with water, like alcohols, glycols, etheralcohols, nitrites, DMSO, DMF, DMA, NMP, THF and acetone, arepurposively used for aqueous applications.

Preferred organic solvents are aliphatic alcohols, glycols,etheralcohols, dimethylsulfoxide (DMSO), dimethylformamide (DMF),dimethylacetamide (DMA), N-methylpyrrolidone (NMP), aliphatic oraromatic ketones, aromatic hydrocarbons, carboxylic acid esters andaliphatic polyethers.

Glycerol, ethylene glycol and propylene glycol are especially preferredorganic solvents.

The ink compositions according to the invention may additionallycomprise one ore more binder resins (c).

The binder resin serves to immobilize or increase the adhesion of thecolorant, particularly on non-porous articles such as for exampleplastic, metallic materials and glassine materials. Any suitable binderresin can be used. Preferably the binder resin is soluble, dispersibleor emulsifiable in the ink carrier. It is further preferred that thebinder resin has sufficient adhesion to the substrate following thedissipation of the ink carrier.

Examples of suitable binder resins include alkyds, acrylics, acrylates,acrylic latexes, epoxy resins, polyvinylpyrrolidon, polyurethanes, vinylresins, polyvinyl acetates, polyvinylalcohol, polyvinylbutyral, PVC,chlorinated rubber, polycaprolactone, polyethyleneglycol esters of fattyacids, polyalkenes such as polyethylene, polypropylene and polybutylene,polystyrene, poly-α-methylstyrene, copolymers of polyethylene with vinylacetate, polysulfones, polyesters, polysiloxanes, styrene butadiene,styrene-acrylic copolymers, polyacrylics, polyacrylates such aspolymethylacrylate and polymethylmethacrylate, nitrocellulose andcellulose ethers such as methylcellulose and ethylcellulose, andmixtures thereof.

The compositions according to the invention are well compatible with allconventional aqueous and solvent-based printing formulations known inthe art. Some of these printing formulations are commercially available.

In preferred ink compositions according to the invention the binderresin (c) is selected from the group consisting of polyacrylics,polyacrylates, polyurethanes, polyurethane-acrylates, styrene-acryliccopolymers, nitrocellulose and ethylcellulose.

Aqueous ink jet formulations containing polyacrylics, polyacrylates,polyurethanes or polyurethane-acrylates as binder resin (c) areparticularly preferred.

In the compositions according to the present invention the amounts ofcomponents (a) and (b) and where appropriate (c) can vary within wideranges.

Preferred compositions contain 0.01 to 70.0%, more preferably 0.05 to30% and in particular 0.1 to 10.0%, by weight of component (a) and 30.0to 99.99%, more preferably 70.0 to 99.95% and in particular 90.0 to99.9%, by weight of component (b), based on the total amount ofcomponents (a)+(b).

High amounts of component (a) are usually well-suited for the inkconcentrate in solvent-based applications.

The amount of component (c) depends on the printing application whichdetermines the required viscosity and the required fixation propertiesto the substrate. Preferably, the amount of component (c) is 0.5 to 70%,more preferably 1 to 50% and in particular 1 to 30%, by weight, based onthe total amount of components (a)+(b)+(c).

Further ingredients which may be present in the ink compositionsaccording to the invention are e.g. natural or synthetic thickeners,dyes, pigments, optical brighteners, acids, bases and/or salts to adjustthe pH to the desired value, anionic, nonionic or cationic surfactants,antifoaming and antifrosting agents, biocides, bactericides,electrolytes, humectants, fragrance, softeners and fixing agents.

Especially preferred are compositions according to the inventionadditionally containing (d) one or more colorant(s).

Suitable colorants are the well-known pigments and dyes includingmixtures of different pigments and dyes.

The ink compositions according to the invention can be prepared by anysuitable method known to those of ordinary skill in the art. Forexample, the components of the composition can be combined and mixed ina suitable mixer or blender.

The present invention further provides a system for marking items with ahidden mark which can only be revealed under UV exposure comprising aprinting means for printing said mark on said items, wherein saidprinting means employs an ink composition as described above.

The marking system may additionally include a transport system to carrythe items to the printing means. For example, the items can be carriedunder the print head of an ink jet printer using a conveyor belt.

The present invention further relates to a method for providing a hiddenmark on an object, preferably a textile material, comprising applyingonto said object an ink composition as described above and removing allor substantially all of said ink carrier by evaporation or absorptioninto or onto said object.

The hidden mark can also be hidden into a visible mark, either byoverprinting onto a visible mark or by using a coloured formulation, asdescribed in the working examples.

The hidden mark can be made visible by subjecting the object to excitingradiation having a wavelength of from about 275 nm to about 400 nm; theemitted fluorescent radiation is in the visible range, preferably fromabout 450 nm to about 700 nm. The emission spectrum contains a sharpemission peak.

The invention can be applied in all customary printing applications likeflexographic printing, offset printing, screen printing, ink-jetprinting, transfer printing and textile printing.

A wide variety of substrates can be marked with the fluorescing colorantaccording to the invention such as textile materials (wool, cotton,leather, silk, polyamide, polyester, mixed fibers, polyacrylonitrile,lycra), cellulosic materials (wood, paper), metals as well as plasticmaterials (polyethylene, polypropylene, polyethylene terephthalate,polybutylene terephthalate), porous materials, any other substratecoated with a receiving polymeric or oligomeric matrix, or which can becoated with a polymeric or oligomeric matrix as provided by the bindersystem (c).

The present invention makes it possible to apply colourless or colouredhidden marks to various colourless, white, pale coloured or darkcoloured substrates, which can be revealed under UV exposure. Thecompositions according to the invention distinguish from analogous priorart compositions by outstanding luminescence quantum yield, long-lastingluminescence and high luminescence intensity.

The following Examples illustrate the invention.

Ink Composition A:

Concentrate of compound XII in 1,2-propylene glycol

1 g of compound XII (prepared according to WO96/20942) is dissolved in99 g of 1,2-propyleneglykol under heating at 100° C. for 1 hour. Theclear yellow solution is allowed to cool down and after filtration(clarification) provides the stable ink Composition A which exhibits anintense red luminescence under UV light. This concentrate can be furtherused in either solvent based or aqueous based conventional or high-tech(ink-jet) printing formulations for paper, textile, leather, wood,plastic or other compatible substrates.

EXAMPLE 1

A colourless aqueous ink-jet ink is prepared by diluting 6 parts byweight of ink Composition A with 4 parts by weight of a standardpolyurethane-acrylate aqueous ink-jet ink formulation. The abovedescribed quasi-colourless formulation is printed on white paper,coloured paper, white or coloured textiles and results in a strong redluminescence under UV exposure.

EXAMPLE 2

A pigmentary yellow aqueous ink-jet ink is prepared by diluting 1 partof ink Composition A with 1 part of a standard commercialpolyurethane-acrylate pigmentary yellow aqueous ink-jet ink formulation.

The above-described yellow formulation was printed on white paper,coloured paper, white or coloured textiles and resulted in a strong redluminescence under UV exposure.

EXAMPLE 3

A pigmentary red aqueous ink-jet ink is prepared by diluting 3 parts ofink Composition A with 1 part of a standard commercialpolyurethane-acrylate pigmentary red aqueous ink-jet ink formulation.The above-described red formulation is printed on white paper, colouredpaper, white or coloured textiles and results in a strong redluminescence under UV exposure.

1. An ink composition containing (a) a compound of formula IL_(m)-Ln³⁺(Ch⁻)_(n)  (I),  wherein Ln represents a lanthanide, Ch⁻ is anegatively charged ligand containing at least one UV absorbing doublebond, n denotes 3 or 4, m denotes a number from 1 to 4, in case n is 3,m denotes a number from 1 to 4 and L is a neutral monodentate orpolydentate nitrogen-, oxygen- or sulfur-containing UV absorbing ligandwith the exception of 2,2′-bipyridyl or, in case n is 4, m denotes 1 andL is a single-charged cation; and (b) a liquid ink carrier.
 2. An inkcomposition according to claim 1 containing as component (a) a compoundof formula II, III or IV

L_(m) ^(o)-Ln³⁺[R₁—O⁻]_(n)  (IV), wherein Ln represents a lanthanide, ndenotes 3 or 4, m denotes a number from 1 to 4 in case n is 3, m denotesa number from 1 to 4 and L is a neutral monodentate or polydentatenitrogen-, oxygen- or sulfur-containing UV-absorbing ligand with theexception of 2,2′-bipyridyl or, in case n is 4, m denotes 1 and L is asingle-charged cation, R₂, is hydrogen or C₁-C₆alkyl, and R₁ and R₃ areeach independently of the other hydrogen, C₁-C₆alkyl, CF₃, C₅-C₂₄aryl orC₄-C₂₄heteroaryl.
 3. An ink composition according to claim 1 containingas component (a) a compound of formula I wherein L is anitrogen-containing ligand.
 4. An ink composition according to claim 1containing as component (a) a compound of formula I, wherein L is acompound of formula V, VI, VII, VIII or IX

wherein R₄, R₅ and R₆ are each independently of the other hydrogen,halogen, C₁-C₆alkyl, C₅-C₂₄aryl, C₆-C₂₄aralkyl, C₁-C₆alkoxy,dialkylamino or a cyclic amino group and R₇ is hydrogen, C₁-C₆alkyl,C₅-C₂₄aryl or C₆-C₂₄aralkyl.
 5. An ink composition according to claim 4containing as component (a) a compound of formula I, wherein L is acompound of formula V, VI, VII, VIII or IX wherein R₄, R₅ and R₆ arehydrogen, methyl, pyrrolidino or dimethylamino.
 6. An ink compositionaccording to claim 1 containing as component (a) a compound of formulaI, wherein Ln is Eu, Tb or Dy.
 7. An ink composition according to claim2 containing as component (a) a compound of formula II, III or IVwherein R₁ and R₃ are methyl, t-butyl, n-pentyl or phenyl.
 8. An inkcomposition according to claim 2 containing as component (a) a compoundof formula II, wherein R₂ is hydrogen.
 9. An ink composition accordingto claim 1 containing as component (a) a compound of formula X, XI, XII,XIII, XIV or XV


10. An ink composition according to claim 1 containing as component (b)one or more organic solvents or a mixture of water and one or moreorganic solvents.
 11. An ink composition according to claim 10containing as organic solvent an aliphatic alcohol, an etheralcohol,glycol, dimethylsulfoxide (DMSO), dimethylformamide (DMF),dimethylacetamide (DMA), an aliphatic or aromatic ketone, an aromatichydrocarbon, a carboxylic acid ester or an aliphatic polyether.
 12. Anink composition according to claim 10 containing as organic solvent awater-miscible solvent.
 13. An ink composition according to claim 10containing as organic solvent ethylene glycol or propylene glycol. 14.An ink composition according to claim 1 additionally containing (c) abinder resin.
 15. An ink composition according to claim 14 wherein thebinder resin (c) is selected from the group consisting of polyacrylics,polyacrylates, polyurethanes, polyurethane-acrylates, styrene-acryliccopolymers, nitrocellulose and ethylcellulose.
 16. An ink compositionaccording to claim 1 containing 0.01 to 70.0% by weight of component (a)and 30.0 to 99.99% by weight of component (b), based on the total amountof components (a)+(b).
 17. An ink composition according to claim 4containing 0.5 to 70% by weight of component (c), based on the totalamount of components (a)+(b)+(c).
 18. An ink composition according toclaim 1 containing additionally (d) one or more colorants.
 19. A systemfor marking items with a hidden mark which can only be revealed under UVexposure comprising a printing means for printing said mark on saiditems, wherein said printing means employs an ink composition accordingto claim
 1. 20. A method for providing a hidden mark on an objectcomprising applying onto said object an ink composition according toclaim 1 and removing all or substantially all of said ink carrier byevaporation or absorption into said object.
 21. A method according toclaim 20 wherein said object is a textile material.